An air brake system for a vehicle such as a bus, a truck, a trailer, other heavy vehicles or the like includes a brake shoe and a drum assembly operated by an actuator assembly which is driven by selectively applying a compressed air.
A general air brake actuator includes both a service brake actuator for driving a brake in a general running state by applying a compressed air and a spring-type emergency brake actuator for driving a brake when an air pressure is released.
The emergency brake actuator includes a compression spring for pressing the brake when an air pressure is released.
The emergency brake actuator is also called a spring brake.
The air-operated brake actuator may be a piston type actuator or a diaphragm type actuator.
In a diaphragm type actuator, a brake actuator and two air-operated diaphragm brake actuators are generally disposed in a tandem vehicle form, and this diaphragm type actuator includes an air-operated service brake actuator for operating a general brake and a spring brake actuator for operating a parking brake or an emergency brake of a vehicle.
The service brake actuator and the spring brake actuator include a housing having an elastic diaphragm, which divides the inside of the housing into two distinguishable fluid chambers.
Meanwhile, the piston brake actuator is operated in the same way as above except for the diaphragm, and the piston reciprocates in a cylinder for operating the parking brake of a vehicle.
In a general service brake actuator, the service brake housing is divided into a pressure chamber and a push rod chamber.
The pressure chamber is connected to a source of the compressed air to allow movement of fluid between them, and the push rod chamber has a push rod mounted thereto and is connected to a brake assembly to introduce or discharge a compressed air into or out of the pressure chamber by reciprocating the push rod into or out of the housing which drives or releases the brake.
In a general spring brake actuator, the spring brake housing is divided into a pressure chamber and a spring chamber.
Both ends of the pressure plate opposite to each other are located at the spring chamber between the diaphragm and the strong compression spring in contact with the housing.
The actuator rod extends through the pressure plate and the diaphragm to the pressure chamber and extends from the service brake actuator through a partition wall which divides the spring brake actuator, as well known in the art.
An end of the actuator is connected to the pressure chamber of the service brake actuator to allow movement of fluid between them.
When the parking brake is operated, the pressure of the spring brake actuator is discharged from the pressure chamber, and the strong compression spring pushes the pressure plate and the diaphragm toward the partition wall between the spring brake actuator and the service brake actuator.
At this location, the actuator rod connected to the pressure plate is pushed to operate the parking brake or the emergency brake and forces the vehicle not to move.
In order to release the parking brake, the pressure chamber is closed against the atmosphere, and the compressed air expands the pressure chamber and moves the diaphragm, and also moves the pressure plate toward the opposite ends of the housing of the spring brake actuator so that the strong compression spring is introduced into the pressure chamber of the spring brake actuator.
Meanwhile, in a process of operating the parking brake to maintain a parking state, in a process of releasing the parking brake to maintain a running state, or in a process of operating the foot brake in a running state, in order to facilitate smooth operations of these processes, channels should be provided to ensure air flow among a plurality of chambers of the air-compression brake actuator, namely a spring chamber, a pressure chamber and a service chamber.
In an existing spring-type air-compression brake actuator using an air pressure, the difference in air pressure, caused by expansion and shrinkage of the chambers in each process, is solved by introducing an external air. For this, a plurality of chambers including a spring chamber, a pressure chamber and a service chamber should be connected through an external tube, or the plurality of chambers should be connected to the outside through a separate tube. However, this configuration needs a complicated channel structure.